Pressurized water reactor plant with improved jet pump arrangement



Allg 24, 1955 M. BoGAARDT ETAL 3,202,584

PRESSURIZED WATER REACTOR PLANT WITH IMPROVED JET PUMP ARRANGEMENT 2Sheets-Sheet 1 Filed Jan. 23, 1962 Aug. 24, 1965 M. BoGAARDT ETAL3,202,584

PRESSURIZED WATER REACTOR PLANT WITH IMPROVED JET PUMP ARRANGEMENT 2Sheets-Sheet 2 Filed Jan. 23, 1962 United States Patent Office 3,202,584Patented Aug. 24, i965 I '3,202,584 PRESSURIZED WATER REACTUR PLANTIMPRUVED JET PUMP ARRANGEMENT Maarten Bogaardt, The Hague, Wouter G.Bonsel and Matthijs Muysiren, Scheveningen, and Wilhelmus W. Nijs,Rijswiik, Netherlands, and Abraham Bahhout, Brussels, elgium, assignorsto Reactor Centrum Nederland, The Hague, Netherlands, an institute ofthe Netherlands Filed Jan. 23, '1962, Ser.'No.`16S,f156 Claims priority,application Netherlands, Jan. 26, 1961,

11 Claims. (Cl. l176-61) This invention relates to fluid circulationapparatus and methods. Y Y

The invention is particularly concerned with pressurized water reactorplants of the type comprising a closed circuit which is completely lledwith water underv pressure acting bothvas a coolant and as a moderator,a casing containing a plurality of spaced substantially verticalelongated fuel elements, which together constitute the core of a nuclearreactor, a heat exchanger for the transfer of the useful heat producedin said c,o"re. said casing and said heat exchanger forming part of saidclosed circuit, and means for forcing water through said circuit and invertical direction through passages-`dened between said"fuel elements. YH

In conventional plants of the type provided with; a pressurized waterreactor,'the amount `of water ilowing in "a given time through thereactor core is equal to'thatilowing in an equal time through anassociated outer circuit provided with a heat exchanger. Since themaximum allowable temperature of the Water in the core is limited by`the possible occurrence of local burning of the reactor parts, each corestructure requires apredetermined minimum water current through thecore. The more compact volume thereof, the more water will have toilowtper unit of time through the core and also through the outer i parto thecircuit. This requires a strong pump for the :circulation of the waterVand decreases the thermal oliiciency of the plant. The decrease of thiseiiciency may be somewhat reduced by making Vthepconduits of the outercircuit and the total passage `of the associated heat exchanger of largecross-section; Thusit appears that` a reduction of the size of a reactormust be coupled with an enlargement of the outer part of the plant andwith the provision of a high pressure for Vwater ow. `This in turnresults in a' considerably moreex'pensive requirement for material andequipment.

Another disadvantage of knownzpressurized water re- `actor plants isthat, 'when the pump stops, the Water in f to propel vessels.

A further object of the invention is to provide improved methodsrelating to` fluid circulation in pressure iluid circulation systems.According to oneembodiment of the invention, a jet p pump is provided ina casing, there being a jet tubewhich 1 `forms part of the associatedcircuit and which is directed in such manner as Vto force'water towardskthe water inlet end of the associated core. The suction opening of saidpump is arranged so as to draw water from the water outlet end of thecore, the arrangement being such as to allow a part of the flow of waterpassing through the core to be Vforced by said jet pump through acsecondcircuit which is entirely inside the casing. The arrangement further issuch as to keep, at full load of the reactor, that means at theallowable maximum continuous load, the ratio between the quantity ofwater passing per unit of time through the core from its inlet to itsoutlet and the quantityf of water flowing per unit of time through thecircuit outsidethe casing between 1.5 and 4.

In such a plant only a portion `of the cooling water owing through thecore is forced through the outer part of the iirst circuit. This makesis possible to decrease considerably Ithe size of said outer part andmoreover to use a pump of smaller power. The reduction of the size ofthe outer circuit also saves expensive heavy water if this is used as acoolant. Further there is more freedom the core and that through theouter part of therst circuit lying between 1.5 and 4. Above 4 either thevelocity of the current of water through the core is toohigh,

v which results in too heavy losses due to the resistance,

`a core is and the-more heat thus produced per unit of` or the ow ofwater through the'outer part of the circuit is too small, Vwhichrequires too great a cooling of the water in the heat exchanger, wherebyunallowablethermal Astresses may be set up and the efficiency isunfavorably affected. Below 1.5 the gain obtained by the measuresrecommended in accordance with the invention is not compensated any moreby the Vmore complicated construction `of the plants.

The increase of the amount of water forced per unit Vof time through thecore has `firstly the advantage that the .1 higher, since the :danger'ofburning in the hottest zones appears to be less when the waterpassing'through the core has a greater velocity. Another advantage ofplants constructed in accordance with the invention is that the jet pumpor set of jet pumps operating in parallel does not form an obstacle forthe second circuit within the casing so that,.when the main pump fordriving the water fails or serious leakage occurs, the water in the corewill not come lto a stand still but continues to flow due to the thermo-Asiphon action in the inner circuit. That is why the danger -oflocalized melting of the core is considerably reduced.

Moreover, jet pumps do not have movingparts, which may lead tostagnation. Finally, the regulation of the plant by the control of theinner circuit is more sensitive so that a better stabilization of theoperation of the core is possible. Y

The reactor may be advantageously so constructed as Vto permit the innersecond circuit to be closed outside the core. This makes it possiblereducing the sizeof the core and providing a large return path for thewater4 without -the necessity of making the casing inetliciently big.Also,

a better control of thetemperature of said water is thereby possible.

In order to obtain a better mixing and distribution of the cooler waterfrom the outer part yof the rst circuit, after it has entered thecasing, and the hotter water cir-V culating within `the casing, a mixingcompartment maybe provided in the casing in front of the inlet end ofthe core,

-tl1e part of the cirst circuit outside the casing.

. ments of a pressurized water reactor plant.

Yment.

lThe position and/or the capacity of each of the jet pumps may be sochosen as to result in the correlation Vof the local intensity of theflow of water passing through the core to the local power density of thecore.

Instead of being positioned immediately or by means of the mixingcompartment in front of the inlet end of the core the jet pump or theset of jet pumps operating in parallel may be accommodated in the spacewhich with respect to 4the axis of the core is provided in the casingradially at the side of the core. A -greater freedom of control of thetwo circuits may be obtained when the jet tube ofthe or each jet pump isconnected to a branch of In said branch, an automatically controllablechoke member may be provided, of which the aperture is controlled independence on the drop of pressure along the core or on the variationper unit of time of said pressure drop. It is also possible to connecttwo or more jet pumps, or two or more sets of jet pumps operating inparallel, in series, the

Yjet tubes of which pumps are connected to parallel branches of the partof the rst circuit outside the casing. When at the side of the core butinside the casing `a free space containing jet pumps is used for closingthe inner second circuit, the casing may advantageously be shaped as asphere or an ellipsoid in order to obtain a whirl of natural form. Sucha shape of the casing increases both the resistance to pressure and theinsulation thereof. If the core is also shaped as a sphere or anellipsoid, the fuel elements may extend in concentric hyper-boloids ofrevolution in order to improve the water circulation within the casing.In that case the elements and the passages may be straight if they arepositioned in the generatrices of said curved surfaces.

Regarding the use of jet pumps to obtain second cir- .cuits entirelywithin the casings of the boiling Water type of nuclear reactor, theinner circuits thereof are used for the control of the energy generatedby the associated cores and depend on the moderating operation, or inother words on the water-steam ratio, of the coolant in the cores. Thissecond circuit is not meant for an increase of thermal eiiiciency or formaintaining said eflciency when the dimensions of the plant are reduced.In known boiling water reactor plants, the ratio between the quantity ofwater forced through the core and the quantity of steam owing throughthe outer circuit must be much more than 4 to have a reasonable eifectand to enable the control aimed at withina large range.

The invention will be elucidated with the aid of the accompanyingdrawing which illustrates various embodi- In the drawings:

FIG. 1 is a partly vertical sectional View, partly elevational view of apressurized water reactor plant according tothe invention;

FIG. 2 is a vertical sectional View of a variant of a portion of thereactor shown in FIG. 1;

FIG. 3 is a vertical sectional view of a second variant of a portion ofthe reactor illustrated in FIG. 1;Y

FIG. 4 is partly a vertical sectional View, partly an .elevational viewof a portion of a pressurized water reactor plant which is provided withanother reactor;

FIG. 5 is a vertical sectional view of a variant of the reactor shown inFIG. 4;

. .and4 of the above-mentioned ratio.

FIG. 7 is a vertical sectional view of a spherical reactor; and

FIG. 8 is a graph showing dependence of the thermal effect of the planton the circulation ratio of the water.

Y In FIG. ,1,V arpressure resisting casing 1 contains a reactive coreconsisting of vertical fuel elements 2. These fuel elements are spacedfrom one another and placed in tube-like cells of a honeycomb structureH, which is open at both ends. Saidv elements are spaced from the wallsof said cells and kept erect by studs S so that passages 3 for themoderating cooling water are formed therebetween and the core may beconsidered as a water permeable structure.

The ca-sing forms part of a water circuit having an outer portionconsisting of conduits 4 and 5, a heat exchanger 6 and a pump 7. Thecasing and the remaining part of the circuit are filled with water underhigh pressure.A

The pump forces the water upwards through the core 2. Within the casing,the jet tubes 8 on manifold M of a set of jet pumps operating inparallel are provided -in the said circuit. The `suction openings 9 ofsaid jet pumps are in open communication with the space 10 contained inthe casing radially outwards of and at the side of the core and with theupper or outlet end of the core through said space.

During operation, the jet pumps force the water along a second circuitindicated by `arrows 11 and entirely contained within the casing andparticularly within the cylindrical member C which may be included bysaid casing. Consequently, the quantity of water flowing per unit ofVtime through the passage 3 of the core is greater than the quantity ofwater which is forced per unit of time through the outer circuitincluding elements 4, 6, 5 and 7. The ratio m between the two quantitiesmust lie between 1.5 and 4 in order to obtain an optimal thermal eifectn of the plant. If the thermal efficiency n of a plant according to theinvention is plotted against the circulation ratio, that means the ratiom between the intensity of the water current through the core and thatthrough the outer circuit, `a graph is obtained as shown in FIG. 8. Fromthis graph it appears that the optimum lies between the value 1.5

The variant illustrated in FIG. 2 differs from that according to FIG. 1in that the inner jet pumps 8', 9 have a greater capacity than the outerjet pumps 8, 9. Due to this, the current of water through the portion ofthe core where the heat production is greatest will be greater than thatpassing through the remaining part of the core. As afconsequencethereof, the current of water through the core will be better adjustedto the local power intensity of the core.

In FIGS. 1 and 2, the jet pumps 8, 9 and 8', 9 are mounted immediatelyin front of the inlet ends of the passages 3. However, it may beimportant to improve the mixing of the colder water supplied by the pump7 with the hotter water of the second circuit 11 before it enters thecore. To this end, a mixing compartment 12, into which the jet pumps 8,9 and 8', 9 open, is provided in front of the inlet end of the core`(see FIG. 3). In this case, there is more freedom as to the selectionof the number and the position of the jet pumps than with theembodiments shown in FIGS. 1 and 2. Such pumps need not be mounteddirectly in front of the cooling passage of the core.

In FIG. 4 a plurality of jet pumps 13, 14 operating in parallel areprovided in the space 1G at the side of the core and in the neighborhoodof the upper end thereof. An annular ring conduit R couples said jetpumps to pump 7. The advantages of this arrangement of the jet pumps arethat a large mixing space is automatically obtained, the height of thereactor may be reduced and the water leaving the core may be morereadily drawn away.

In the embodiments shown in FIGS. 1-4, it is somewhat diiicult tocontrol the inner and the outer circuit r separately, since to that endthe jet tubes of the jet pumps must be mounted for adjustment withrespect to their suction openings. To improve this situation, the jetpumps 13, 14 of the plant illustrated in FIG. 5 are connected to abranch 15 of the outer circuit which is directly connected to the lowerend of the casing 1. Provided in said branch 15 is a controllable valveor an adjustable choke member 16, by means of which the jet pumps 13, 14may be controlled. Moreover, the conduit 17 ofthe outer circuit, whichis directly connected to the casing, has a gradually narrowing portionfollowed by a widening portion, in such a manner, that said conduit endsas a venturi-tube. Due to this construction a suction force is exertedon the inner circuit. It will be obvious that the member 16 makes itpossible to control the jet pumps independently from the water currentflowing in the outer circuit.

In the embodiment shown in FIG. 6, the mixing compartment 12 and the jetpumps 8, 9 and 8', 9 connected to the conduit 17 are provided, in themanner shown in FIG. 3, in front of the inlet end of the core and thejet pumps 13, 14 are positioned, in the manner illustrated in FIG. 5, atthe sideof the core. In this case the jet tubes S, 8 and 13 areconnected to the parallel branches 17 and 15 of the outer portion of thecircuit and the jet pumps 8, 9 and 8', 9 on the one hand and the jetpumps 13, 14 on the other hand are connected in series with respect tothe inner circuit 11 of the water. In this manner, it is easy to makethe water current of the inner circuit considerably stronger than thatwhich flows through the circuit outside the reactor casing. Also, inthis case, the choke member 16 is provided in the branch 15. The passagearea of said member is controlled in dependence on the absolute value oron the variation of the pressure drop in the core. To that end, pressuresensitive pick-ups 19 are mounted both in the neighborhood of the inletand in that of the outlet end of the core and are connected throughconduits 2d with a measuring instrument 21 reacting on pressuredifferences or on pressure variations and controlling through aconnection 22 the choke member 16.

FIG. 7 shows a variant of the plant illustrated in FIG. 5. Therein thereactor is constructed as compactly as possible, to which end the casing23 is made spherical and the shape of the core approximates that of asphere. The spherical shape has, in addition to the advantage of agreater resistance to pressure and a smaller heat radiation, thefavorable elect that in the equator thereof a 4 sages may extend inconcentric hyperboloids of revolution. If said elements and passages arepositioned inthe direction of the straight generatrices of said curvedsurfaces they may also be straight.

What is claimed is:

1. A pressurized water reactor plant comprising a vertical casing, aplurality of vertical elongated fuel elements in said casingconstituting a nuclear reactor core, means supporting said fuel elementsin spaced relation to define a plurality of substantially verticalpassages, a heat exchanger, conduits interconnecting said casing andsaid heat exchanger to form a closed circuit, said circuit beingcompletely lilled with Water acting both as a coolant and as amoderator, a main pump in one of said conduits having a pressure outletand a suction inlet and adapted to circulate water through said closedcircuit, said core having a lower inlet end and an upper outlet end anddelning together with the casing an upper space, a lower space and aspace surrounding said core and interconnecting said upper space andsaid lower space outside the core and inside said casing, and a jet pumpdisposed in said space surrounding the core, said jet pump including ajet tube connected to the pressure outlet of said main pump, the Vjetpump having a suction inlet directed towards the upper space in thecasing into which the outlet end of the core opens, the jet pump havinga pressure outlet directed to- Wards the lower space in the casing towhich the inlet end of the core is in communication.

2. A pressurized water reactor plant as claimed in claim 1, in whichsaid jet pump is disposed adjacent the outlet end of the core in thespace surrounding the core and contained in the casing.

3. A pressurized water reactor plant as claimed in claim 1, comprising asecond jet pump, the latter pump being disposed in the lower space ofthe casing below the inlet end of the core, said second jet pumpincluding a jet tube, which is also connected to the pressure outlet ofthe main pump, the pressure side of the second jet pump being directedtowards the inlet end of the core and the suction side of said secondyjet pump communicating through the lower space of the casing with thespace thereof surrounding the core and'containing each rst jet pump.

4. A pressurized water reactor plant as claimed in claim 3, ycomprisingflow control means in the conduit extending from the pressure side ofthe main pump to the jet tube of the rst kjet pump and 'automaticcontrol means operatively coupled to said flow control means, saidautomatic control means being responsive to water pressure drop alongthe core of the nuclear reactor.

5. A pressurized water reactor plant as claimed in claim 3, comprisingflow control means in the conduit extending from the pressure side ofthe main pump to the jet tube of each first jet pump and automaticcontrol means operatively coupled to said llow control means, saidautomatic control means being responsive to variation per unit of timeof water pressure drop along said core.

6. A pressurized water reactor plant as claimed in claim 1, comprising aplurality of jet pumps including the rst said pump in the space of thecasing surrounding the core, a common manifold for said jet pumps, saidjet pumps operating in parallel and the jet tubes of said jet pumpsbeing connected to said common manifold which is Iconnected to thepressure side of the main pump.

7. A pressurized water reactor plant as claimed in claim 1, in which thecasing has la spherical shape, the fuel elements constituting thenuclear reactor core being straight elements which define a peripheryconstituting axial hyperboloid surfaces of revolution that substantiallyconform with the shape of said casing, said surfaces of revolutionhaving an axis which coincides with the vertical axis ofthe casing.

8. A pressurized water reactor plant as claimed in claim 1, in which thecasing has an ellipsoid shape, the fuel elements constituting thenuclear reactor core being straight elements which define a peripheryconstituting coaxial hyperboloi-d surfaces of revolution thatsubstantially conform with the shape of said casing, said surfaces ofrevolution having an axis which coincides with the vertical axis of thecasing.

9. A Imethod of operating a pressurized water reactor Which has avertical casing and a liquid permeable vertical nuclear reactor core inthe casing defining a lower inlet space, an upper outlet space, and aspace surrounding the core providing communication between the upperspa-ce and the lower space, said method comprising circulating a coolingliquid through the casing and externally thereof through a closed4circuit in which 'heat is absorbed by the cooling liquid in the reactorcore while heat is extracted from the cooling liquid externally iof thecasing, a portion of the cooling liquid being forceably recirculated'inthe casing along a path extending ldownwardly from the upper space tothe lower space through said space surrounding the core and thenupwardly through said core again and back to the upper space to maintaina ratio between the quantity of cooling liquid passing per unit timethrough the core and the quant-ity of cooling liquid passing per unittime through the casing at between 1.5 and 4.

lll. A method of operating a pressurized Water reactor which has avertical casing and a liquid permeahlevertical nuclear reactor core inthe casing dening a lower inlet space, .an upper outlet space, and aspace surrounding the core and providing communication between the upperspace and the lower space, said method comprising circulating a coolingliquid along a closed circuit including the casing, the liquid absorbingheat from the reactor core :and transferring the heat externally of thecasingas the liquid completes a passage through said circuit, dividingthe liquid inflow to the casing to cause liquid to directly flow intosaid casing upwardly through the core from the inlet space to the outletspace while concurrently causing liquid to ow downwardly in the spacesurrounding the casing from a zone adjacent the upper space to the lowerspace and thence upwardly through the core, recirculating `the liquidwithin said casing along a path extending from the upper space to thelower space through the space surrounding the casing and then upwardlythrough the core hack to the upper space to maintain a ratio between thequantity of liquid passing per unit time through the core and thequantity of liquid passing per unit time through the casing at hetween1.5 and 4.

11. A method as claimed -in claim 10 wherein the 'portion of the liquidwhich is introduced in the space surrounding the casing is injected intosaid space under turbulent conditions.

References Cited by the Examiner UNITED STATES PATENTS REUBEN EPSTEIN,Acting Primary Examiner.

CARL D. QUARFORTH, Examiner.

1. A PRESSURIZED WATER REACTOR PLANT COMPRISING A VERTICAL CASING, APLURALITY OF VERTICAL ELONGATED FUEL ELEMENTS IN SAID CASINGCONSTITUTING A NUCLEAR REACTOR CORE, MEANS SUPPORTING SAID FUEL ELEMENTSIN SPACED RELATION TO DEFINE A PLURALITY OF SUBSTANTIALLY VERTICALPASSAGES, A HEAT EXCHANGER, CONDIUTS INTERCONNECTING SAID CASING ANDSAID HEAT EXCHANGER TO FORM A CLOSED CIRCUIT, SAID CIRCUIT BEINGCOMPLETELY FILLED WITH WATER ACTING BOTH AS A COOLANT AND AS A MODERATORA MAIN PUMP IN ONE OF SAID CONDIUTS HAVING A PRESSURE OUTLET AND ASUCTION INLET AND ADAPTED TO CIRCULATE WAER THROUGH SAID CLOSED CIRCUIT,SAID CORE HAVING A LOWER INLET END AND AN UPPER OUTLET END AND DEFININGTOGETHER WITH THE CASING AN UPPER SPACE, A LOWER SPACE AND A SPACESURROUNDING SAID CORE AND INTERCONNECTING SAID UPPER SPACE AND SAIDLOWER SPACE OUTSIDE THE CORE AND INSIDE SAID CASING, AND A JET PUMPDISPOSED IN SAID SPACE